Powder composition for bright dipping zinc and cadmium



United States Patent E as.

3,171,765 POWDER COMPOSITION FUR BRIGHT DIPPING ZIN AND CADMIUM Kenneth P. Bellinger, Ellington, and Eugene G. Chapdelaine, Hazardville, Coun., assignors to Conversion Chemical Corporation, Rockyille, Conan, a corporation of Connecticut No Drawing. Filed Oct. 4, 1962, Ser. No. 228,251 12 Claims. (Cl. res-2e The present invention relates to the chemical brightening of metals and more particularly to a powder composition for preparing a bath to chemically brighten the surfaces of zinc, cadmium, and alloys thereof.

The term zinc surfaces as used hereinafter refers to surfaces of zinc and zinc-base alloy articles and other metallic articles having a coating of zinc or zinc-base alloy such as produced by hot-dipping or electroplating.

The term cadmium surfaces as used hereinafter refers to surfaces of cadmium and cadmium-base alloy articles and other metallic articles having a coating of cadmium or cadmium-base alloy such as produced by electroplating.

Heretofore, the most widely used baths for brightening zinc and/ or cadmium have been prepared by the addition of various components to solutions of nitric and/or sulfuric acids so as to provide an aqueous acid solution containing chromate, fluoride and/ or sulfate, and nitrate ions. Such baths are used extensively throughout the metal fabricating industry in large volumes. The use of liquid acids in making up such bright dipping baths is subject to a number of objectionsnot the least of which is the fact that the proportion or relationship of the ingredients is oftentimes critical for optimum operation as in an automatic apparatus, and the measuring of the acid and other components is oftentimes relegated to unskilled workers. This problem becomes particularly acute when periodic make-up additions are necessary during use of the bath. Additionally, the use of liquid acids requires expensive containers for shipment thereof and upon which deposits are oftentimes charged so that the containers must be returned and records must be kept. Clearly, freight costs for the water content of liquid acids can be quite substantial. Moreover, safety factors in handling and storing liquid acids often present a considerable problem.

It is the aim of the present invention to provide a selfcontained dry powder formulation for addition to water to produce a highly effective bath for the chemical brightening of cadmium surfaces and zinc surfaces and which is convenient and safe to ship and handle, relatively economical in operation and precontrolled in the optimum proportion of essential ingredients so as to provide a balanced bath composition.

Another aim is provide such a self-contained dry powder formulation wherein the speed of the bath action upon the metal workpieces may be varied readily by varying the amount of powder formulation added to water.

It has now been found that the foregoing and related aims can be readily attained by use of a dry powder formulation consisting essentially of a chromate compound, an activating salt selected from the group consisting of fluorides, sulfates and the combination thereof, and an acid-nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfarnic acid, and sulfamic acid and nitrate salts of inorganic bases wherein the acid-nitrate component is of suificient acidity to provide a pH of about 0.5 to 3.8 upon addition of the composition to water in amounts suflicient to provide about 0.1 to 10.0 grams per liter of chromate ion (calculated as CrO A leveling agent such as borate ion or acetate ion may also be incorporated to control the bath opera- 'ice tion. The bath thus prepared may be used at ambient or low elevated temperatures with the time of immersion necessary for brightening the workpiece varying with the concentration and temperature of the bath.

More particularly, the powder compositions of the present invention contain essentially 1.0 to 10.0 percent by weight of chromate compound; 1.0 to 35.0 percent by Weight of an activating salt selected from the group consisting of fluorides, sulfates and the combinations thereof; up to 5.0 percent by weight of a leveling agent selected from the group consisting of borates and acetates; and 50.0 to 98.0 percent by weight of an acid-nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases.

Generally, the acid-nitrate component should provide sufficient nitrate ion to provide a nitrate to chromate ion weight ratio in excess of 5:1 and preferably above 10:1. High weight ratios tend to produce iridescence and/or significantly reduce corrosion protection developed by the composition so that the effective upper limit is 40:1 and preferably 30:1. In practice, a weight ratio of 15 to 25:1 has proven particularly effective for permitting wider variation in the amounts of powder composition added to water to vary the dip times.

The activating agent preferably is in an amount sufficient to provide a fluoride and/ or sulfate ion to chromate ion weight ratio of about 1 to 5:1, and preferably about 1521.0 to 30:10 Higher ratios tend to produce excessive iridescence or dullness in the resultant surface finish. In some baths, it is desirable to employ both fluoride and sulfate in combination for optimum brightening action.

Leveling agents are desirably incorporated in the bath for pH control and control of the rate of bath action to achieve optimum brightening while reducing the criticality of the control of time and temperature of treatment as is particularly desirable in automatic processing operations. Additionally, they may serve to harden the film. As little as 0.05 grams per liter may produce a beneficial effect, and amounts up to about one-half the weight of chromate compound may sometimes be advantageously employed. Generally, amounts equal to about one twentieth to one-fifth the weight of chromate compound have proven preferable for most compositions. It should be noted, however, that corrosion protection will generally be reduced by increasing the concentration of the leveling agent. Although various other compounds have been proposed for this purpose, borates and acetates have proven particularly satisfactory both from the standpoint of performance and cost.

Although the baths produced by the compositions of the present invention have been found effective within the pH range of 0.5 to 3.8 depending upon the component salts and the concentration thereof, generally the preferred pH range is 1.0 to 2.5 for both zinc and cadmium. The optimum pH for zinc surfaces is 1.0 to 2.0 whereas treatment of cadmium surfaces appears to be optimum at the slightly. higher pH level of 1.5 to 2.5.

The preferred compositions of the present invention contain about 2.0 to 6.0 percent by Weight chromate compound, 3.0 to 18.0 percent by weight of the activating salt, up to 0.75 percent by weight of the leveling agent, and 75.0 to 95.0 percent by weight of the acidnitrate component.

Although chromate ion is effective over the relatively Wide range of concentration of 0.1 to 10.0 grams per liter, the preferred baths operate within a concentration range of about 0.5 to 5.0 grams per liter. Within this range of the concentration, the speed of bath action can be relatively easily controlled, and the surface finish is more Q uniform during the normal period of use. Generally, the workpieces are immersed in the bath for a period of about five to sixty seconds depending upon the concentration of the bath and the temperature thereof. Although the bath may be operated satisfactorily at low elevated temperatures of up to about 130 degrees Fahrenheit, it is generally preferable to conduct the dipping operation at ambient temperatures of about'60 to 95 degrees Fahrenheit since the speed of operation is more readily controlled. The workpieces are rinsed in cold water and preferably thereafter in hot water to facilitate drying.

The sulfates and'fluorides are added as salts having non-interfering cations. The preferred compounds are alkali metal and ammonium salts, and the acid salts thereof (NaI-IF KHF NH I-IF NaHSO etc.) have proven particularly advantageous in being readily soluble and in providing additional -means of controlling the to water.

The chromate compound which provides the operative chromate'ions in the bath may be chromic acid anhydride (CrO or any soluble salt thereof having a noninterfering cation, including alkali metal and ammonium chromates and alkali metal and ammonium bichromates.

"Similarly, the nitrate salts of inorganic bases may be any amounts depending upon the desired concentration of chromate ion and the desired speed of operation interms of 'dip' time. Of course, the amount of any given powder composition added must be sufficient to provide the desiredpH level so that the percentage of the acidic compH of the bath provided upon addition of the composition pound(s) in the acid-nitrate component should be selected to provide a bath falling within the desired pH range over arange of varying'concentration. Generally,

the dry powder formulation will be addedto water in an amount equal to about 10.0 to 100.0jgrams' per liter, and thep-H of'the resultant bath may vary to some degree with the concentration of the acidic compound therein.

Since-the baths are corrosive, the tanks and handling equipment should be fabricated from-acid-resistant material 'to avoid contamination such as rigid polyvinyl chloride or glass fiber-reinforced resin. The dry powder formulations are not in themselves corrosive but should be transported in suitable containers that will minimize the likelihood of inadvertent contact with water or excessive amounts of moisture.

Specific examples of self-contained dry powder compositions which have proven particularly advantageous in the practice of the present invention are as follows:

Percent by weight Indicative of the relative operating limits for component ion concentration in the bath is the test data in the following table wherein zincplated steel but-tons of about I ls-inch diameter were immersed-inbaths-containing the indicated amounts of components for about twelve seconds with agitation.

TABLE Sodium Sodium Urea Panel Chromate, Acid, Fluo- Nitrate, Finish g./l. ride. g./l. g. /l.

1.1 2. 3 0.0 Dull. 1.1' 2. 3 10.0 Do. 1. 1 2. 3 18. 0 Semibright. 1. 1 2. 3 20.0 Bright. 1.1 2. 3 40. 0 Do. 1.1 2. 3 5f). 0 Bright, Iridescent. 0.0 2. 3 30. 0 Dull. 0.6 2. 3 30.0 Bright, Iridescent. 0.9 2. 3 30.0 Bright. 1. 5 2. 3, 30. 0 D0. 1.8 2. 3 30. 0 Semibright. 2. 4 2. 3 30.0 Bright, Iridescent. 2. 7 2. 3 30.0 ull. 1.1 0.0 30.0 Do. 1. 1 0. 5 30. 0 Semibrlght. 1. 1 1. 25 30.0 Bright. 1. 1 3. 25 30. 0 Do. 1, 1 3. 75 30. 0 Semibright. 1. 1 4. 25 30.0 Bright, Iridescent. 1. 1 6. 25 30.0 D0.

Exemplary of the efficacy of the present invention are the following specific examples wherein baths were prepared by addition to water of dry powder components in accordance with the present invention.

Example 1 A dry powder formulation was prepared containing 3.2 percent by-weight sodium chromate, 6.8 percent by weight sodium acid fluoride and 90.0 percent by weight .urea nitrate.

In one liter of water at ambient temperature was dissolved 33.4 grams of the above powder formulation to produce an acid'bath having a pH measured at 1.9 (using a reference standard of pH 1.1). A steel button having an electroplated zinc coating and about 1% inch in diameter was immersed therein with agitation for about twelve seconds and then rinsed in cold water. The resultant finish was clear bright. A 2 inch x 3 inch steel panel having an electroplated zinc coating thereon was similarly treated and also developed a clear bright finish. A drop of 5.0 percent by weight aqueous lead acetate solution placed upon the test panel did not turn the metal black for seventy-five seconds, indicating an extremely high degree of corrosion protection.

A similar test panel having an electroplated cadmium coating was similarly treated and developed a bright finish with a slight white fog. This finish gave a value of twentyfive seconds in the lead acetate test, indicating a high degree of corrosion protection.

In a second liter of water was dissolved 66.8 grams of the powder formulation (twice the quantity) to provide a ,bath having apHof 1.9. After immersion therein for twelve seconds, a zinc-plated test panel had a clear bright surface finish which gave a value of sixty seconds in the lead acetate test. A cadmium-plated steel test panel, upon similar immersion developeda bright surface with a slight white fog which gave a value of .fifteen seconds in the lead acetate test.

In a third liter of water was dissolved 16.7 grams of the dry powder formulation (one-half the quantity) to provide a bath having a pH of 1.9. A zinc-plated test panel developed a clear bright finish which gave a value of sixty seconds in the lead acetate test. A cadmium-plated test panel developed a bright finish with a slight .white fog which :gavea value of twenty seconds in the lead acetate .test. 7

Example 2 A bath was prepared by adding to one liter of water the following dry powder components: 1.6 grams of potassium 1 Generally, a value of ten seconds is considered to indicate a high degree of corrosion protection since an untreated panel will turn black immediately.

bichromate, 2.0 grams sodium acid sulfate and 15.0 grams urea nitrate. The pH of the bath was determined at 1.1.

After immersion in the bath for about twelve seconds at room temperature with agitation, a bright finish with a blue caste was produced upon a 2 inch X 3 inch steel panel having an electroplated zinc coating. The finish gave a value of forty-five seconds in the lead acetate test, indicating a very high degree of corrosion protection.

Example 3 A bath was prepared by dissolving in one liter of water 0.8 gram chromic acid anhydride (CrOg). 2.7 grams sodium acid fluoride, 28.0 grams sodium nitrate, and 13.7 grams sulfamic acid. The resultant bath had a pH of 2.1.

A zinc-plated steel test panel was immersed therein for about twelve secondswith agitation and then rinsed. The resultant finish was clear bright and gave a value of 120 seconds in the lead acetate test. A similar test panel having an electroplated cadmium coating was immersed therein and developed a bright finish with a slight fog which gave a value of twenty seconds in the lead acetate test.

A second bath was prepared by adding only one-half the amounts of powder components described above and a third bath was prepared by adding twice the amounts of dry powder components. Both baths had a pH of 2.1. A zinc-plated test panel treated in the second bath developed a clear bright finish which gave a value of 120 seconds in the lead acetate test.

A zinc-plated test panel immersed in the third bath developed a clear bright finish which gave a value of over 120 seconds in the lead acetate test.

Example 4 A bath was prepared by dissolving in one liter of water 1.9 grams sodium chromate, 0.7 gram sodium hydrogen sulfate, 0.4 gram sodium sulfate, 2.8 grams of sodium fluoride and 30.0 grams of urea nitrate. The resultant bath had a pH of 1.8.

A zinc-plated steel panel immersed therein for about twelve seconds at room temperature developed a clear blue finish which was found to give a value of twenty-five seconds in the lead acetate test.

Example 5 A bath was prepared by dissolving in one liter of water 1.1 grams of sodium chromate, 2.3 grams of sodium acid fluoride, 20.0 grams of urea nitrate and 10.0 grams of sulfamic acid. Additional baths were prepared by doubling and halving the amounts of the above components respectively. Each of the resultant baths had a pH of 1.7.

Upon immersion therein for twelve seconds with agitation, zinc-plated test panels each developed a bright finish with a slight fog which gave a value of sixty seconds in the lead acetate test.

Example 6 A bath was prepared by dissolving in one liter of water 1.1 grams of sodium chromate, 2.3 grams of sodium hydrogen fluoride, 16.0 grams urea nitrate, and 10.0 grams of sodium nitrate. The resultant bath had a pH of 1.4.

Upon immersion therein for twelve seconds with agitation, a zinc-plated test panel developed a clear bright surface finish which gave a value of 120 seconds in the lead acetate test. A cadmium-plated test panel developed a bright finish with a fog and gave a value of five seconds in the lead acetate test.

The concentration of powder components was reduced to one-half in a second bath and doubled in a third bath.

A zinc-plated test panel immersed in the bath of reduced strength developed a clear bright finish with a very light blue caste and gave a value of sixty seconds in the lead acetate test. A cadmium-plated test panel developed a bright finish with a slight iridescence which gave a value of fifteen seconds in the lead acetate test.

A zinc-plated test panel immersed in the more concentrated third bath developed a clear bright finish and gave 6 a value of seconds in the lead acetate test. A cadmium-plated panel developed a bright finish with a slight fog which gave a value of five seconds in the lead acetate test.

Thus, it can be seen from the foregoing detailed specification and specific examples that the present invention provides a novel self-contained dry powder composition for addition to Water to produce a highly elfective bath for the chemical brightening of zinc and cadmium surfaces. The dry powder composition is convenient and safe to ship and handle and is relatively economical in operation. It provides a precontrolled proportioning of the essential components of the brightening bath so as to ensure a balanced bath composition even when the responsibility for make-up additions is delegated to unskilled employees. The dry powder composition further enables the variation of the speed of bath action upon the metal workpieces merely by varying the amount of powder composition added to the bath and the resultant concentration of the essential ions.

Having thus described the invention, we claim:

1. A self-contained dry powder composition for addition to water to provide an acid bath for brightening zinc surfaces and cadmium surfaces consisting essentially of 1.0 to 10.0 percent by weight of water-soluble chromate compounds; 1.0 to 35.0 percent by weight of a water-soluble activating salt selected from the group consisting of fluorides, sulfates and the combination thereof; up to 5.0 percent by weight of a water-soluble leveling agent consisting of borates and acetates; and 50.0 to 98.0 percent by weight of a water-soluble acid-nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases, said acid-nitrate component being of sufficient acidity to provide a pH of 0.5 to 3.8 upon addition of the dry powder composition to water in amounts sufficient to provide 0.1 to 10.0 grams per liter of chromate ion, said dry powder composition having a nitrate ion to chromate ion weight ratio of 5.0 to 40.0: 1.

2. The dry powder composition in accordance with claim 1 wherein said acid nitrate component will provide a pH of 1.0 to 2.5 upon addition to water.

3. The dry powder composition in accordance with claim 1 wherein the nitrate ion to chromate ion weight ratio is 10 to 30:1.

4. The dry powder composition in accordance with claim 1 wherein the activating ion to chromate ion weight ratio is 1 to 5:1.

5. A self-contained dry powder composition for addition to water to provide an acid bath for brightening zinc surfaces and cadmium surfaces consisting essentially of 1.0 to 10.0 percent by weight of water-soluble chromate compound; 1.0 to 35.0 percent by weight of a water-soluble activating salt selected from the group consisting of fluorides, sulfates and the combination thereof; up to 5.0 percent by weight of a water-soluble leveling agent consisting of borates and acetates; and 50.0 to 98.0 percent by weight of a water-soluble acid nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases, said acid-nitrate component being of sufficient acidity to provide a pH of 1.0 to 2.5 upon addition of the dry powder composition :to water in amounts sulficient to provide 0.1 to 10.0 grams per liter of chromate ion, said dry powder composition having a nitrate ion to chromate ion weight ratio of 10 to 30:1 and an activating ion to chromate ion weight ratio of l to 5:1.

6. The dry powder composition in accordance with claim 5 wherein said acid-nitrate component is urea nitrate.

7. The dry powder composition in accordance with claim 5 wherein said acid-nitrate component is urea nitrate and the nitrate salt of an inorganic base.

:8. A self-contained dry powder composition for addition to water to provide an acid bath for brightening zinc surfaces and cadminum surfaces consisting essentially of 2.0 to'6.0 percent by weight of water-soluble chromate compounds; 3.0 to 18.0 percent by weight of a water-soluble activating salt selected from the group consisting of fluorides, sulfates and the combination thereof; up to 0.75 percent'by weight of .a Water-soluble leveling a'gent consisting of borates and acetates; and 75.0 to 95.0 percent by :weight of a water-soluble acid nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases, said acid-nitrate component being of sufficient acidity to provide a pH of 1.0 to 2.5 upon addition of the dry powder composition to water in amounts sufficient to provide 0.1 to 10.0 grams per liter of chromate ion, said dry powder composition having a nitrate ion toichromate ion weight ratio of 10 to 30:1 and an activating ion to chromate ion weight ratio of 1 to 5:1.

9. The method of brightening Zinc and cadmium Workpieces comprising providing a dry powder composition consisting essentially of 1.0 to 10.0percent by weight of water-soluble chromate compound, 1.0 to 35.0 percent by weight of a water-soluble activating salt selected from the group consisting of fluorides, sulfates and the combination thereof, up to 5.0 percent by weight of a watersoluble leveling agent consisting of borates and acetates, and 50.0 to 98.0 percent by weight of a water-soluble acid nitrate component selected from the group consisting of urea nitrate, urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases; dissolving said dry powder composition in water to provide a bath containing 0.1 to 10.0 grams per liter chromate ion and having a pH of 0.5 to 3.8; and immersing in said bath for a period of about five to sixty seconds workpieces having a surface of metal selected from the group consisting of zinc, cad.- mium and alloys thereof, said bath producing a relatively bright surface finish thereon.

10. The method in accordance with claim 9 wherein said bath has a nitrate ion to chromate ion weight ratio of 5 to 40:1 and an activating ion to chromate ion weight ratio of 1 to 5:1.

11. The method in accordance with claim 9 wherein said bath has a nitrate ion to chromate ion weight ratio of 10 to 30:1 and an activating ion to chromate ion weight ratio of 1 to 5:1 and wherein said bath has a pH of to 2.5.

12. A self-contained dry powder composition for addition to water to provide an acid bath for brightening zinc surfaces andcadmium surfaces consisting essentially of 1.0 to 10.0 percent by weight of water-soluble chromate compound; :1.0 to 35 .Opercent by weight of awater-solu; ble activating salt selected from the group consisting of fluorides, sulfates and the combination thereof; up to 5.0

' percent by weight of a water-soluble leveling agent consisting of borates and acetates; and 50.0 to 98.0 percent by: weight of a Water-soluble acid-nitrate component selected from the group consisting of urea nitrate,urea nitrate and nitrate salts of inorganic bases, urea nitrate and sulfamic acid, and sulfamic acid and nitrate salts of inorganic bases, said acid-nitrate component being of sufiicient acidity to provide a pH of 0.5 to 3.8 upon addition of the dry powder composition to Water in amounts suflicient to provide 0.1 to 10.0 grams per liter of chromate ion, said dry powder composition having a nitrate ion to chromate ion weight ratio of 5 .0 to 40.0:1 and an activating ion to chromate ion weight ratio of 1.0 to 5 .0: 1.

References Cited by the Examiner UNITED STATES PATENTS 2,186,579 1/40 Dupernellet a1. 15620 2,904,413 9/59 Hampel 156-2O XR 2,904,414 9/ 59 Ostrander et a1. 156-20 3,072,516 1/63 Bellinger et al l56-20 ALEXANDER WYMAN, Primary Examiner. EARL M. BERGERT, JACOB STEINBERG, Examiners. 

9. THE METHOD OF BRIGHTENING ZINC AND CADMIUM WORKPIECES COMPRISING PROVIDING A DRY POWDER COMPOSITION CONSISTING ESSENTIALLY OF 1.0 TO 10.0 PERCENT BY WEIGHT OF WATER-SOLUBLE CHROMATE COMPOUND, 1.0 TO 35.0 PERCENT BY WEIGHT OF A WATER-SOLUBLE ACTIVATING SALT SELECTED FROM THE GROUP CONSISTING OF FLUORIDES, SULFATES AND THE COMBINATION THEREOF, UP TO 5.0 PERCENT BY WEIGHT OF A WATERSOLUBLE LEVELING AGENT CONSISTING OF BORATES AND ACETATES, AND 50.0 TO 98.0 PERCENT BY WEIGHT OF A WATER-SOLUBLE ACID NITRATE COMPONENT SELECTED FROM THE GROUP CONSISTING OF UREA NITRATE, UREA NITRATE AND NITRATE SALTS OF INORGANIC BASES, UREA NITRATE AND SULFAMIC ACID, AND SULFAMIC ACID AND NITRATE SALTS OF INORGANIC BASES; DISSOLVING SAID DRY POWDER COMPOSITION IN WATER TO PROVIDE A BATH CONTAINING 0.1 TO 10.0 GRAMS PER LITER CHROMATE ION AND HAVING A PH OF 0.5 TO 3.8; AND IMMERSING IN SAID BATH FOR A PERIOD OF ABOUT FIVE TO SIXTY SECONDS WORKPIECE HAVING A SURFACE OF METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM AND ALLOYS THEREOF, SAID BATH PRODUCING A RELATIVELY BRIGHT SURFACE FINISH THEREON. 